Add 2021 day 5 puzzles

2021/puzzle-05-01.cc

@@ -0,0 +1,68 @@
+//
+// Created by Matthew Gretton-Dann on 05/12/2021.
+//
+
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <regex>
+#include <string>
+
+using Point = std::pair<unsigned, unsigned>;
+
+auto get_points(std::string const& s) -> std::pair<Point, Point>
+{
+  static std::regex re{R"((\d+),(\d+) -> (\d+),(\d+))"};
+  std::smatch m;
+  if (!std::regex_search(s, m, re)) {
+    std::cerr << "Unable to interpret: " << s << "\n";
+    std::exit(1);
+  }
+  return {{std::stoul(m.str(1)), std::stoul(m.str(2))},
+          {std::stoul(m.str(3)), std::stoul(m.str(4))}};
+}
+
+auto main() -> int
+{
+  std::string line;
+  std::map<Point, unsigned> vents;
+  while (std::getline(std::cin, line)) {
+    auto [pt1, pt2] = get_points(line);
+    std::cout << "{" << pt1.first << ", " << pt1.second << "} -> {" << pt2.first << ", "
+              << pt2.second << "}: ";
+    if (pt1.first == pt2.first) {
+      unsigned y1{std::min(pt1.second, pt2.second)};
+      unsigned y2{std::max(pt1.second, pt2.second)};
+      std::cout << "vertical:\n";
+      while (y1 <= y2) {
+        auto [it, success] = vents.insert({{pt1.first, y1}, 1});
+        if (!success) {
+          ++(it->second);
+        }
+        ++y1;
+      }
+    }
+    else if (pt1.second == pt2.second) {
+      unsigned x1{std::min(pt1.first, pt2.first)};
+      unsigned x2{std::max(pt1.first, pt2.first)};
+      std::cout << "horizontal:\n";
+      while (x1 <= x2) {
+        auto [it, success] = vents.insert({{x1, pt1.second}, 1});
+        if (!success) {
+          ++(it->second);
+        }
+        ++x1;
+      }
+    }
+    else {
+      std::cout << "sloped\n";
+    }
+  }
+
+  auto danger_count{
+    std::accumulate(vents.begin(), vents.end(), unsigned{0},
+                    [](auto a, auto const& it) { return a + (it.second >= 2 ? 1 : 0); })};
+
+  std::cout << "Danger spots: " << danger_count << '\n';
+  return 0;
+}